Aerosolized Mycobacterium tuberculosis (MTB) is readily transmitted from person to person. Mycobacteria infect the distal alveoli where they replicate unfettered in the face of innate responses. As adaptive T cell immunity develops, MTB growth is controlled but bacilli are not eradicated. The interactions between T cells and MTB infected antigen presenting cells (APC) are central for the organism to evade/resist host immunity to establish latent infection. In this application in response to RFA-HL-10-015 Systems Biology Approach to the Mechanisms of TB Latency and Reactivation we bring together a multidisciplinary team of experts in proteomics, computer science, bioinformatics, genetic epidemiology, epidemiology, immunology, lung biology and pulmonary medicine coupled to access to a unique set of cohorts of epidemiologically and clinically well characterized persons with the spectrum of MTB exposure, infection and disease in the US, Uganda and S. Africa, in order to apply novel systems biology approaches to latent MTB infection. Recent studies suggest that proteomic approaches aimed at identifying protein-protein interaction networks result in the identification of functional sub-networks with a role in disease pathogenesis. We propose to apply this approach to the analysis of latent MTB infection (LTBI) in humans, and to link proteomic results with parallel studies using human genetic and systemic chemo-/cytokine approaches to understanding MTB pathogenesis. The general hypothesis of this proposal is that proteomic seeds identify sub-networks of proteins that differentiate persons at different stages of MTB infection and disease, and provide insight into the mechanism(s) responsible for progression from LTBI to active TB. The aims are: Aim 1: To determine dysregulated protein-protein interaction sub-networks in mononuclear phagocytes and CD4+ T cells of persons in households heavily exposed to MTB who do not become infected compared to those with LTBI who do not progress to disease and those who develop TB. Aim 2: To determine the relationship between protein-protein interaction sub-networks to whole genome and targeted gene analyses, and peripheral chemo-/cytokine responses detected by multiplex chemo-/cytokine assays in the same population as in Aim 1. Aim 3: To determine which of the protein-protein interaction and chemo-/cytokine sub-networks analyzed in Aims 1 and 2 are most relevant for lung CD4+ T cells and macrophages from persons with LTBI. This proposal combines access to unique clinical specimens (peripheral blood cells, plasma, broncho- alveolar lavage specimens) from epidemiologically well characterized persons with MTB infection in US, Uganda and South Africa with experts in the use of proteomics, genetic epidemiology and cytokine biology for a multidisciplinary systems biology approach to LTBI and its progression to active TB. PUBLIC HEALTH RELEVANCE: Systems biology is ideally suited to analyze the complex interaction between humans and M. tuberculosis (MTB), the cause of tuberculosis (TB), and is particularly powerful when applied to tissues from persons in different stages of MTB exposure, infection and disease. Using systems biology to find key host proteins disturbed by MTB exposure or infection allows us to identify persons at risk for progression to active TB and find out what we need to be naturally or through vaccination protected against TB.